(Writing some extra posts because Mohamed mentioned I'd stopped...)
It's ironic that WebKit introduced the
<canvas> API, but since Firefox
is the one with market share it gets to drive the implementation:
Yes, unfortunately firefox violates the spec in a way that people seem to depend on. I've already emailed whatwg about this. It's safe to move to the firefox behaviour as it's a relaxation of existing API.
(from bug 27187)
It's a trivial thing, really, but I feel like there might be a broader lesson there about how specifications anneal.